In defence of Zevran he only has nothing to say if you don't get his approval rating up, and that is the same with many of the characters, Sten is one who really springs to mind: "Care to talk?" "No". First time I never got Sten up high enough for him to divulge about his sword. There are some things Zevran will only talk about if you are romanced but I still got the confession about his reason for taking the mission as a friend.
No need to defend Zevran, but he just is only half the fun without the flirting. And I had maxed his approval, like with the others, too. I always play for full approval because in DA your people either love (or hate for DA2) you or you are locked out of content. For example he won't tell me anything about the assumed betraying but falsely accused love of his. And that is an important part of his character after all. Still, I only learn it when romancing him. Similarly I will only get the cookie scene, which explains everything about Sera, if I am on good terms with her already anyway.
So a little off topic. Does anyone know if it is better to make Cole human rather than a spirit? I always end up making him a spirit because Solas says so... 
There is no "better" I think. One way you leave him be what he is but condemn him to stay isolated, the other way you change him but help him get integrated. It's like Bull's quest, he will be content with both. It is your moral choice, you "win" or "lose" the same either way.
Aaaah, Minister Bellise. So that's the noble you can screw! I was wondering about that. How exactly does one come to this arrangement, exactly? Completely out of curiosity you understand. One must protect their ambassador, after all. XD
That's fairly simple: by being a shameless flirt. Whatever, whoever, you flirt your way through Thedas and all off a sudden they don't want your money or connections anymore but your body alone.